Printed wiring boards (PWBs) holding electronic components have been used in the past in various equipment. A particular problem arises in the use of such equipment when the equipment is subjected to high vibration and shock environments. In the case of electronic fuzing for military applications such as projectiles and bombs, many varied electronic parts must be made to survive and function in severe environments, frequently as high as 30,000 g's and 30,000 revolutions per minute. In transportation, the increased use of electronics often subjects critical control and monitoring devices to high vibration and shock environments.
Prior art printed wiring boards subjected to high stress loading conditions aforedescribed frequently used thick conformal coatings of a compliant plastic or epoxy material. Another method used in the prior art was solid potting. In solid potting the PWBs are placed within a housing and the entire system is potted into a solid assembly. A further prior art method consisted of controlled potting, wherein a potting mold is placed over a complete PWB and the potting material is applied. After curing of the potting, the mold has to be removed and cleaned for use on the next PWB.
The problem with prior art potted PWBs used in projectile fuzing was that the components when subjected to gravity levels in excess of 30,000 g's simply shear off the PWB due to their own induced weight. Prior art conformal coating of PWBs frequently require quality assurance inspectors to make judgement calls on whether the proper amount of potting has been used, the average thickness of the coating and whether the coating provides the proper fillet and radii sizes for each component and what is the maximum acceptable void. This inspection procedure is expensive and not always reliable.